Crosslinked polymers such as rubbers are not recyclable as such, because the crosslinking or the vulcanization is irreversible, in contrast to thermoplastic polymers. Thus, worn tyres of motor vehicles and of heavy lorries and worn rubber pipes must be ground up and employed as filler. Applicant has discovered that the incorporation of these ground rubbers (referred to as "powdered rubber waste" in the text which follows) in combination with a specific copolymer, into bitumens, allows the properties of the bitumens to be improved. In particular the ring-and-ball temperature is increased and the penetration is reduced without its viscosity being increased too much.
EP 305225 describes bitumens to which have been added 8 to 10% by weight of rubber powder, 4 to 6% by weight of a heavy oil of naphtheno-aromatic nature and 2 to 3% of a catalyst. The catalyst is chosen from polymers containing ethylenic unsaturation, already recommended for incorporation into sulphur-vulcanized bitumens intended for road surfacings, for example polyisoprenes, polybutadienes, ethylene-vinyl acetate, butadiene-styrene, etc.
EP 448425 describes a process of extrusion of bitumens and of 20 to 95% by weight of grinding residues. The grinding residues are mixed beforehand with the ground bitumen and a compatibilizing agent, which may be a copolymer of ethylene, of an unsaturated ester and either of maleic anhydride or of glycidyl methacrylate. The whole is extruded and can then be employed as additive to road bitumen. These grinding residues are defined as being all the inorganic and organic materials originating from the grinding or shredding of motor vehicle carcasses, of household electrical appliances and of industrial waste.
These prior arts have not taken into account the excessively large increase in the viscosity and, above all, have not paid attention to storage stability, an essential condition for the utilization of road binders on work sites.